The invention relates to a method for reducing the noise in the drive train of a motor vehicle when in neutral. The motor vehicle has an automatic transmission or a manual transmission with a controllable oil pressure supply and/or automatic starting clutch.
At the present time the power in the drive train of motor vehicles is transferred between the engine sided drive unit and the transmission input shaft by way of a spline connection. This spline connection can connect the engine sided drive shaft to the transmission input shaft either directly or through an interposed dual mass flywheel (which should be regarded as a part of the engine sided drive unit). Such dual mass flywheels are used predominantly for damping the rotational irregularities in the drive train between the crankshaft and the transmission input shaft, so that any amplitudes of vibration of the engine can be filtered out. This spline connection between the engine sided drive unit (with or without a dual mass flywheel) and the transmission input shaft usually has a clearance fit due to technical reasons related to assembly.
When in neutral, the rotational irregularity of the engine may cause a frequent engaging and disengaging of the tooth flanks of the gear tooth system in the spline connection exhibiting a clearance fit and located between the engine sided drive unit and the transmission input shaft.
This situation generates noises that are also known under the term “engine idle knock.” Under some circumstances this noise may give rise to complaints.
In order to suppress such noises, measures have already been implemented in the direction of mechanical modifications. However, such mechanical solutions are complicated and expensive during production and implementation.
Therefore, the object of the invention is to provide a low cost solution for reducing the idling noises in the spline connection having a clearance fit.
This and other objects are achieved with a method for reducing the noise in the drive train of a motor vehicle having an automatic transmission or a manual transmission with a controllable oil pressure supply and/or automatic starting clutch, wherein the engine sided drive unit is connected to the transmission input shaft by a spline connection and the noises in the drive train are caused by the clearance fit in the spline connection between the engine sided drive unit and the transmission input shaft. The method adapts the transmission control for reducing the noise when in neutral.
The method according to the invention is intended, in particular, for motor vehicles having automatic transmissions, such as so-called dual clutch transmissions, where a spline connection is arranged at the interface between the drive unit and the transmission. However, it also lends itself well to vehicles having manual transmissions with a controllable oil pressure supply and/or automatic starting clutch. This spline connection connects the engine sided drive unit or, more specifically the drive shaft, to the transmission input shaft by way of a spline connection. As explained above, the engine sided drive unit can comprise a dual mass flywheel for damping rotational irregularities. Since the spline connection between the engine sided drive unit and the transmission input shaft usually has a clearance fit due to technical reasons related to assembly, the invention proposes for the purpose of reducing the noise, caused by the clearance fit in the spline connection, that the transmission control be adapted when in neutral such that the noise development can be eliminated or at least reduced. A purely software based implementation of the noise reduction does not incur any additional manufacturing costs in production.
It is advantageous to adapt the actuation of the transmission when in neutral in such a way that an increased torque is transmitted via the spline connection. This feature prevents the disengagement of the tooth flanks (a state that leads to noise development) or at least greatly reduces it.
There are a number of implementation possibilities for increasing the transmitted torque by adapting the transmission control. The measures proposed below relate to software based solutions that can be carried out predominantly in automatic transmissions that are in neutral position or park position.
In a first possible embodiment of the method according to the invention, the transmission control can be adapted when in neutral in such a way that the pump receiving torque of a hydraulic pump, which is provided for the hydraulic actuation, is increased. The system pressure is advantageously increased in order to increase the pump receiving torque of the hydraulic pump.
As an alternative or in addition to this measure, the transmission control can also be adapted when in neutral in such a way that an increase in the drag torque transmitted from the clutch is attained. That is, when in neutral the drag torque is increased in a targeted manner. Such an increase in the drag torque can be achieved, for example, by increasing the amount of cooling oil in the clutch. At the same time it is advantageous to ensure the slip in the clutch by, for example, engaging a gear stage of the transmission associated with this clutch.
As an alternative or in addition, a predetermined pressure value can be applied to the clutch assigned to this (part) transmission, assuming that no gear is engaged in the (part) transmission. In this case the pressure value can be variable. The result is a drag torque, which depends on the pressure exerted on the clutch, in the so-called rotary feedthrough unit.
As an alternative or in addition, a synchronization device can be actuated in a predetermined mode (for example, continuously or intermittently) after closing the clutch for transferring a defined torque without an engaged gear. In this case the maximum synchronization torque to be applied to the synchronization device is the clutch torque, where the synchronization has to be able to cope with this load that may be small, but still has to be applied continuously. Therefore, when in neutral the transmission control is adapted in such a way that a predefined synchronization torque is applied by way of a synchronization device to the clutch that is closed when the gear is not engaged. Then the synchronization torque generates a drag torque acting on the spline connection.
If the architecture of the set of wheels makes it possible to engage the reverse gear in a first part transmission and a forward gear in a second part transmission (for example, in dual clutch transmissions), then the transmission control can also be adapted in the respective gear position when in neutral in such a way that a torque, which is corrected by the signed gear change, is applied to both clutches assigned to the aforementioned part transmissions, in order to be finally “torque neutral” at the output. That is, the sum of the resulting clutch torques at the two clutches is approximately zero at the transmission output.
Finally, it is also contemplated to adapt the transmission control when in neutral in order to increase the transmitted torque at the spline connection in such a way that when the park stage is engaged and the gear stage is engaged in the respective (part) transmission, the corresponding clutch is actuated at least so far that the clutch torque transferred from the clutch is large enough to eliminate the noise.
Since the aforementioned measures differ in their capability to increase the transferred torque due to the different boundary conditions (type of transmission, situation, etc.), it is practical to combine the above described individual measures or to apply them in an alternating manner as a function of the situation. This would mean that the individual measures are implemented simultaneously at different points-in-time (thus in succession) and/or in different possible combinations so that the ratio of the measures can move between 0% and 100%. This strategy makes it easy to find transmission and situation specific solutions for reducing the noise when in neutral without having to accept the drawbacks of the individual measures.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.